Andy Murray, Simona Halep and Stan Wawrinka beat the heat with straight-sets wins to reach the third round of a sweltering US Open, while American hope Jack Sock wilted under the punishing conditions, collapsing on court.
Murray triumphed 5-7, 4-6, 6-1, 6-3, 6-1 after his world number 35 opponent had threatened to condemn him to his earliest loss in New York since also making the second round on debut in 2005.
But left-hander Mannarino wilted in the heat and humidity in Arthur Ashe Stadium as Murray's greater freshness and physical condition proved crucial.
Murray goes on to face Brazilian 30th seed Thomaz Bellucci for a place in the last 16.
As courtside temperatures pushed past 100 Fahrenheit (38 Celsius) at Arthur Ashe Stadium, second seeded Halep of Romania wasted little time finishing off Ukraine qualifier Kateryna Bondarenko 6-3, 6-4 in just 76 minutes before escaping to the air-conditioned comfort of the players' lounge.
Fifth-seeded Swiss Wawrinka outslugged gutsy South Korean teenager Chung Hyeon, but still sweated out a 7-6 (6/2), 7-6 (6/4), 7-6 (8/6) second round decision.
Next up for the French Open champion is Ruben Bemelmans of Belgium, who advanced when Sock retired due to cramping while leading 6-4, 6-4, 3-6, 1-2.
Sock had looked in control of the match but began to show signs of distress in the third set, then sent a shock through the crowd when he began to cramp and dropped to the court as medical staff rushed to his aid.
The American grimaced in pain as he was wrapped in ice towels with bags of ice also placed around his body.
A wheelchair was brought out but after several minutes Sock was helped to his feet and, assisted by a trainer under each arm, he limped off the court.
The week-long heat wave has taken a heavy toll at the year's final grand slam with 12 players retiring due to the conditions or because of injuries in the opening round before Sock added his name to the casualty list in the second.
Britain's Johanna Konta delivered the shock of the day but needed three hours and 27 minutes under the blazing sun to complete the upset as she ousted ninth-seeded Spaniard Garbine Muguruza 7-6 (6/4), 6-7 (6/4), 6-2.
"I noticed after the first set - it was incredibly long, but then after I had a couple glances on the clock, I'm like, 'Oh, okay. We have been here for a while.' But we deal with it as best we can," said Konta.
"It was the same for her and the same for a lot of players playing out there at this time.
"Actually, I did have a thought out there ... a conscious thought, 'Would it be really embarrassing if I just toppled over here?'"
Germany's Angelique Kerber, the 11th seed, also took the express route into the third round by taming Italian Karin Knapp 7-5, 6-2 while 20th seed Victoria Azarenka of Belarus was a 7-5, 6-4 winner over Belgium's Yanina Wickmayer.